Blood plasma enters the afferent arteriole and flows into the glomerulus, a cluster of intertwined capillaries. The Bowman’s capsule (also called the glomerular capsule) surrounds the glomerulus and is composed of visceral and parietal layers.

The visceral layer lies just beneath the thickened glomerular basement membrane and is made of podocytes that form small slits in which the fluid passes through into the nephron. The size of the filtration slits restricts the passage of large molecules (such as albumin) and cells (such as red blood cells and platelets) that are the non-filterable components of blood.

These then leave the glomerulus through the efferent arteriole, which becomes capillaries meant for kidney–oxygen exchange and reabsorption before becoming venous circulation. The positively charged podocytes will impede the filtration of negatively charged particles as well.

The process by which glomerular filtration occurs is called renal ultrafiltration. The force of hydrostatic pressure in the glomerulus (the force of pressure exerted from the pressure of the blood vessel itself) is the driving force that pushes filtrate out of the capillaries and into the slits in the nephron.

Osmotic pressure (the pulling force exerted by the albumins) works against the greater force of hydrostatic pressure, and the difference between the two determines the effective pressure of the glomerulus that determines the force by which molecules are filtered. These factors will influence the glomerular filtration rate (GFR), along with a few other factors. Pressures are depicted with the liquid-column gauge, flows through the tubules with the pointer measures and turbines, flow through the vessel walls with width and speed of the dashed moving arrows. This visualised sensors are used also in all other parts of the application.

Student can change resistance of afferent and efferent arteriole and thus control the hydrostatic pressure in glomerular capillaries and GFR. Mean arterial pressure (pressure at afferent arteriole entry) may be also modified. The goal is to explain how the glomerulus maintains constant GFR despite changing arterial pressure by means of changing afferent and efferent arteriole resistance.